1. Field of the Invention
The present invention relates to an ultrasonic motor and an electronic device using the ultrasonic motor, and in particular, relates to an ultrasonic motor using a self-exciting oscillator circuit in a driver circuit of the ultrasonic motor, and to an electronic device using the ultrasonic motor.
2. Description of the Prior Art
Research and development of self-excited oscillator circuits capable of being realized by a small number of parts and having a simple structure, and in their application to small-sized electronic devices, has occurred in recent years. For example, this type of self-exciting oscillator circuit is disclosed in Japanese Patent Application Laid-open No. Hei 9-163769.
A signal amplified by the amplifier circuit is input to the booster circuit through the phase setting circuit and the and the phase regulating circuit. The signal boosted by the booster circuit is applied to an electrode of a piezoelectric element, and the piezoelectric element is excitation driven. A driving signal based on the oscillation of the piezoelectric element is fed back to the amplifier circuit and the piezoelectric element performs self-excited oscillation. As a result, a vibrating member joined to the piezoelectric element vibrates, and a moving member resiliently contacting the vibrating member under a predetermined pressure applied by pressurization means, rotates.
The stop signal generation circuit is a circuit for controlling the operation of the amplifier circuit, and therefore the amplifier circuit stops outputting in accordance with a stop signal. The piezoelectric element stops self-excited vibration, and therefore it becomes possible to arbitrarily stop the rotation of the moving member.
However, when applying a signal generated by the booster circuit to electrode groups formed on a surface of the piezoelectric element in a self-excited oscillator circuit utilizing a conventional booster circuit,the direction of rotation is limited in one direction in order for the signal to be applied to only one electrode group. There is a problem, therefore, in that the ultrasonic motor cannot apply to uses requiring forward and reverse operation by controlling a set position of the ultrasonic motor, such as the opening and closing of a shutter and determining the position of a disc.
An object of the present invention is to obtain an ultrasonic motor which is driven by a self-excited oscillator circuit with a booster circuit which is capable of controlling forward and reverse operation in accordance with an external signal, or an electronic device having an ultrasonic motor to solve the conventional problems.
In order to solve the above stated problem, the present invention is structured by an ultrasonic motor composed of a vibrating member having a piezoelectric element and an amplifying circuit and structures an oscillator circuit for self-excited oscillation of the vibrating member at a predetermined resonance mode, and which drives a moving member by an oscillatory wave generated in the vibrating member, and includes a booster circuit for boosting an electric voltage generated by an amplifier circuit, and outputting a signal to a common electrode formed on one face of the piezoelectric element, and a selection circuit for switching a signal path of a booster signal output from a plurality of electrode groups formed on another face of the piezoelectric element.
In accordance with this, by outputting the signal generated by the booster circuit to the common electrode formed on one face of the piezoelectric element, and by connecting the selection circuit for selecting a rotational direction in the plurality of electrode groups formed in the other side of the piezoelectric element, it becomes possible to control forward and reverse rotational directions by one set of booster circuits. The increase of the number of parts can be suppressed, and an ultrasonic motor having a good efficiency self-exciting oscillation circuit which can supply a booster voltage obtained from the booster circuit to the piezoelectric element as is, without reduction, and an electronic device having the ultrasonic motor, and realizing a forward and reverse capable self-excited oscillator circuit using the booster circuit, along with forming the selection circuit in the electrode side which is not connected to the booster circuit.